Resistance-wire for electric heaters.



R. H. READ.

RESISTANCE WIRE FOR ELECTRIC HEATERS. APPLICATION FILED MAY 28. 1914.

1 1 92,457. Patented July 25, 1916.

UNITED STATES PATENT OFFICE.

ROBERT H. READ, OF WASHINCTON, DISTRICT OF COLUMBIA, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW'. YORK.

RESISTAE'CE-WIRE FOR ELECTRIC HEATERS.

Specification of Letters Patent.

Patented July 25, 1916.

Original application filed July 19, 1910, Serial No. 572,778. Divided and this application filed May 28, 1914.

Serial No. 841,544.

To all whom it may concern:

Be it known that I, ROBERT H. READ, a citizen of the United States, residing at \Vashington, in the District of Columbia, have invented new and useful Improvements in Resistance-Wires for Electric Heaters, of which the following is a specification.

This invention relates to fireproof insulated resistance wires or elements for electric heaters or the like and is applicable in all cases Where electrically generated heat is utilized or dissipated.

The heating wire is of a type comprising a high resistance core-wire inclosed in a continuous metallic shell or armor and separated therefrom by a firmly packed an nular layer or bed of mineral fireproof insulation in the form of powder. Such wires are alloys varying in specific resistance, but always very high relatively to a good conduetor such as copper, and are therefore adapted for heating work or such as requires a large diffusion or dissipation of energy, as contradistinguished from conducting work where a minimum dissipation of energy is required for reasons of economical operation. With a mineral oxid insulation such as ground flint the temperature may be raised, as the substance has a melting point above 2,000 centigrade and is not at all damaged by temperatures below its melting point. Ground flint, magnesia and many other oxids or compounds do not become conductive when heated, the melting point being so high that they do not become a conductor of the second class (Nernst efl'cct) except at very high temperatures. I may use any highly refractory insulating powder; I prefer, however,

to use ground flint, such as ground quartz or silex because of its cheapness and better thermal conductivity than other oxids or silicates, and which insures a quicker and more desirable operation for heater or rheostat work. Other mineral oxid powders such as magnesia, alumina, emery, or sulfates, or carbonates such as chalk, or silicates such as soapstone, clay or asbestos may be employed. The powder should be finely divided, free from granules to permit even distribution and should pack "well preventing the infiltration of air. I have had excellent results with a form of powder known on the market as silex, which is sold as a polisher of metals and is a pure form of finely divided silica; a good quality of powdermay be made by grinding flint finely and then separating the finer particles by levigation. Before using it should be heated strongly to expel all moisture. A finished core-Wire of high resistance alloy such as German-silver, climax, or a nickel-chr0- mium alloy is surrounded with the powder and telescoped within a seamless metal tube with a good clearance around the wire and powder, and is then reduced in section. The armor may be of the same material as the core-wire or of a metal of the same expansion coefficient so as to avoid strains due to differences in expansion under heat of the core and shell, or in some cases may be of by removing a short piece of the jacket,-

using preferably a revolving knife such as a pipe cutter. A piece of copper wire may be welded to the end of the core-wire, and

a metallic tube filled with powdered flint or with cement pushed over the wire until it bears on the shell. It may be soldered or brazed to the shell, thus making a rigid structure. The powder fills the tube and carries the heat away from the wire, and the copper will not get hot, and may therefore be led directly to a binding post or other circuit terminal. Thus I have an armored or sheathed heater wire in which the shell offers a large surface of exposure to the air or other heat absorbing medium, permitting the passage of a greatly increased Yes Lee

current without overheating and maintaining the resistance core cool throughout its length. a

This application is a division of my application #572,778 filed July 19, 1910 entitled Insulated conductors and process and apparatus for making the same.

In the accompanying drawings Figure 1 shows enlarged an armored wire powdercovered and surrounded by a seamless metallic jacket; Fig. 1 is a cross-section of the same; Fig. 1 shows the wire reduced until the jacket is firmly shrunk upon the filled or covered wire; Fig. 1 shows the wire much reduced under the action of rolls or dies; Fig. 2 shows a. step in the preparation of the heater wire; and Fig. 3 shows the terminal used at the ends of the heater wire.

A metal ribbon or tape 2 is passed to a curling die 3 which gradually forms it into a tube and at the open end is supplied previously heated dry insulating powder of the kind referred to, precautions being taken to provide a uniform supply of the powder as the tape is formed into a tube. A core-wire of high resistance alloy 4: is led axially of the tube being filled and at the same speed of travel. Means are provived for keeping the seam in a right line, as a blade of steel 8 at the front of the die. The seam may be brazed or welded, but good results may be obtained without this treatment as a seamless outer shell of the proper clearance effectually prevent leakage of the powder'by closing tight on the folded tape, the seamless shell preventing any oozing of powder at the seam. The filled tube is slipper into a seamless metallic tube 5 previously drawn down to a size to permit it to be easily slid or telescoped into it. The structure thus provided is then drawn down in dies or otherwise reduced until the desired size is attained, when the powder will be hard packed and the core-wire central.

As will be seen in Fig. l there is a good clearance between the seamless jacket and the powder covered wire core. In Fig. 1 the jacket has been reduced and has been shrunk into intimate contact with the covcred wire, while in Fig. 1 the whole has been very much reduced in section. Such a wire may be reduced or drawn down to a very few thousandths inch in diameter.

I provide a terminal at the end of the corewire so arranged as to provide efiective radiation for the heat and to-prevent metallic contact with the jacket. A simple and effective plan is to lay bare the core by removing a short piece of the jacket, using preferably a revolvingknife such as a small pipecutter. A piece of copper wire 6 may be welded to the end of the core-wire and a metal tube having a porcelain bead '7 shrunk in the end and filled with powdered flint or cement as at 1 slipped over each end of the shell thus making a rigid structure. The powder fills the tube and carries the heat away from the wire, and as the copper will not by reason of its low resistance get hot, it may be led directly to a binding post or other circuit terminal. If brazed seams are or the like comprising a core of high resist-' ance metal, a body of heat refractory insulation surrounding the core, and a metallic armor having the same coefiicient of expansion as the core-wire inclosing the insulation.

2. An insulated resistance wire for electric heaters or the like comprising a corewire of high resistance material, a closely packed refractory insulating powder surrounding the core-wire, and a metallic armor of similar expansion coefiicient inclosing the powder.

3. The method of making a resistance wire for electric heaters or the like c0nsisting in curling a sheet metal tape around a wire of high resistance, causing the tape to close into a long tube surrounding the wire, simultaneously feeding any insulating material into the space between the resistance wire and the tube, then inclosing the tube in a seamless metal jacket, and reducing the whole in cross-section.

4:. A resistance wire for electric heaters comprising a high resistance core-wire surrounded with heat refractory powder insulation, a metal sheath around the core-wire, and insulating means for stopping the ends of the core-wire against leakage of powder.

5. A resistance wire for electric heaters comprising a high resistance core-wire surrounded with heat refractory insulation, a metallic sheath around the core-wire, and an insulating cement between the core-wire and the sheath at the ends of the element.

6. A resistance wire for electric heaters comprising a high resistance core-wire, a closly packed powder of heat refractory, in-

sulating material from which the moisture has been expelled, and an integral metallic armor of a diflicultly fusible metal tightly embracing the insulating material.

7. A resistance wire for electric heaters comprising a high resistance corewire, a closely packed powder of heat refractory insulating material from which all moisture has been expelled, and a seamless metallic armor of a difiicultly fusible metal on the outside holding the insulating material under compression.

8. A resistance wire for electric heaters comprising a high resistance core-wire, a

10 resistance wire, causing the tape to close into Q a long tube surrounding the wire, simultaneously feeding an insulating powder between the wire and tube, then inclosing the tube in a tubular jacket and reducing the whole in section until the powder is firmly 15 compacted on the wire.

ROBERT H. READ; Witnesses:

ED B MGBATH, S. G. HILL. 

